All cracked up!
When I bored the holes into Marilyn’s head. My latest ball-jointed doll, she cracked! So I went on a hunt to find some solutions to cracks. I seem to run into this problem ever time and only crazy people keep repeating the same mistake over and over and expecting a different result. So what do I do- I research. I educate myself and change what I am doing.
Ways to fix cracks:
- You can use a damp sponge to smooth out the hairline cracks.Stoneware you have to just use a stick to push the clay down. If you use a wet sponge, the grog come out. It takes out the fine particles and reveals the grog.
- A stiff paint brush dipped in water and scabbed over the cracks works too.
- Dip the brush in slip for larger cracks.
- Smooth over small cracks with the edge of a needle tool at bone dry. it usually works. if the crack is significant, use vinegar slip that is not too moist .
- Try the deflocculated slip. Way better than vinegar. Look at bottom for recipe.
- The same material used in the original clay work would also be used as the mending material, but it is important to realize that the CONDITION of that mending clay material will be vital to its success.
- Two different materials with two different shrinkage rates are simply NOT gonna hang around together very long. Therefore, since we’re dealing with ceramic materials subject to shrinkage as they move through a firing cycle, it becomes important to use clay in the mending material that has experienced the SAME conditions as that of the original clay work.
- If the damage needing to be fixed is found in clay work that has already been BISQUE fired, then the clay used to make its mending material must also be bisque fired before the patch can be made. On the other hand, if the crack is found in GREENWARE (that is, in clay work that has NOT been bisque fired yet), then the mending material must use clay that’s still in its raw unfired state.
- By matching the shrinkage rates between the original and the mending materials, you will insure that the patch can create a good, stable fit that will not shrink away or sink below the surface level of the original clay around it. This then makes the repair process much easier, since what you see while working out the final appearance of the patch is exactly what you get in its fired result!
- Fern Zeller mentions in her book that she made a porcelain stick to rub into cracks to repair fired porcelain. Roll scrap porcelain, while still moist into a pencil shape. Important to use same porcelain. After stick is fired to cone .019, this partially fired stick can be rubbed over the crack and it will fill the space. Then when the item is taken agai to high heat the crack is fused and disappears.
A lot of this information is available as a free ebook Art Teacher Ceramic Center
Make the deflocculated slip by taking throwing slip and then adding dry trimming scraps until thick. Then a couple of drops of Darvan 811. That thins it, then more dry trimming scraps. Then a bit more 811. Then dry trimming scraps.
A whole bunch of crack fixing recipes:
Try them a see what works for you.
dry clay body 2 part
soda ash or frit 1 part
corn syrup or vinegar enough to make a paste
SPOOZE variation #1 (greenware): Dries very hard
dry clay 1 part
vinegar 1 part
corn syrup 1 part
peroxide a few drops
GREENWARE REPAIR: No amounts listed
a few drops sodium silicate
LEATHERHARD CLAY or GREENWARE REPAIR (no amounts listed)
MAGIC WATER from Lana Wilson: Use to repair greenware, use instead of a joining slip or add to bone dry clay for a deflocculated slip
water 1 gallon
sodium silicate (a liquid) 3 tablespoons (9.5 g)
soda ash 1.5 teaspoons (3 g)
SIMPLE GREENWARE REPAIR submitted by Jan Edwards: Sometimes I’ve been able to repair a crack on greenware, leather hard or dry, by making a “paperclay bandaid” by immersing a strip of toilet paper into slip from your clay body, or making a thick paste of T.P. & slip. Use it & discard the leftovers. Paper clay gets to stink when left around.
REPAIRING BONE DRY WORK submitted by Kim Murton: APT* mixed with dried clay, ground with the wooden end of a feddling knife, works pretty well for cracks that appear after the piece is bone dry. I open up the crack with a needle tool or sharp wooden pointy tool and then fill the crack with the APT mixture. Then I smooth it all out with a rib. No water!
PRESSING & ROLLING– Cracks sometimes appear where noses attach to faces, usually as the piece is drying. Burnish the crack away using a conical wooden tool, pressing and rolling over the crack. This works surprisingly well if you catch the crack before the piece is too dry but just a tad dryer than leather hard.
CRACKED BISQUE REPAIR submitted by Michelle Gallagher: Mix a bit of crushed soft brick into a thick slip paste of the same raw clay body as the bisque fired piece, filling the crack and smoothing it over before applying glaze. This works especially well in joining areas such as handles and seams. I have even repaired glazed pieces in the same way and re-firing a second glaze with some success. If the piece is cracked and heading for the seconds shelf anyway it’s worth a try.
Sairset 1 part
calcined clay body 1 part
glaze (as goopy as possible) 1 part
powdered bisqued clay
a few drops of sodium silicate
GREENWARE & BISQUEWARE FIXES
SPOOZE variation #2: Use to attach anything, leatherhard, bone dry or bisqueware. Keep applying until cracks disappear.
Liquid sugar: any kind, honey, corn syrup, etc 1 part
vinegar 1 part
slip of your choice, any thickness 1 part
FIX-ALL (green or bisque repair): Mix dry, then add water
dry clay body 100
gum (CMC, arabic, etc) 2
neph sy 2
MARX MAGIC MENDER, submitted by Veronica Hughes: I like Marx Magic Mender for repairing greenware up to the bone dry state. However, depending on the clay, it may or may not match the clay color after bisque firing. It’s also useful for filling in small surface cracks on bisqueware. It’s been successful at temperatures as high as Cone 10.
COLEMAN JOINING SLIP cone 6, amounts are by weight
neph sy 15.79
OM 4 ball clay 26.32
silica (200 mesh) 21.05
dry clay body 100g
custer feldspar 2 g
bentonite 2 g
gum arabic 2 g
add water to above mixture until it is a thick paste. Then add:
Darvan 1/8 to ¼ teaspoon
Epsom salt solution ¼ teaspoon
*Darvan is available at many ceramic suppliers.
*To make the Epsom salt solution, start with a small amount of water. Add Epsom salt until the water will dissolve no more salt.
Add water until you have a thick cream consistency. The gum arabic will rot if stored for a length of time, you may want to freeze Score No More when not in use.
HJALMARSON’S ADHERING SLIP “A” cone 10, amounts are by weight
ball clay 30
Mix the dry ingredients with a liquid consisting of:
For each pint of slip, add one teaspoon of CMC gum in a gel form (add dry CMC gum to water to make a gel)
Preparing Slip Mixture for Mending and Attaching: Pour fresh slip into container; Add APT-II Ceramic Enhancer into slip until it begins to thicken to a consistency of cake batter; If Slip Mixture becomes too thick for attaching or mending, thin back with slip – not water (Adding water will increase shrinkage); Unused Slip Mixture may be stored in an airtight sealed container for several days. Add more slip if it becomes too thick; If Slip Mixture is left open to air, it will dry and become greenware.
*APT-2 Ceramic Enhancer is available at many ceramic suppliers. The following are instructions for using APT-2 from their website:
REPAIRING GLAZED WORK submitted by Richard Armstrong: Use an epoxy putty stick to adhere the broken parts. These can be found at any hardware store. They are about 4 to 5 inches long and 3/4 of an inch in diameter. Typically they are a two-part epoxy product that is reddish with a gray center. Cut through with an industrial knife and kneed until a uniform color. It is moldable for a few minutes and sands well. The next challenge is to match the glaze with paint. You can either paint the whole object or go for the match. The last stage is to spray it with a clear or satin cover, homogenizing the whole piece.
Grout-Cracks that happen after the glaze fire just fill with grout. Find a color that matches the clay body fairly well. The crack is repaired but not hidden.
REPAIRING ALREADY-FIRED WORK submitted by Penelope Dews: Here are some ways for fixing cracks in sculpture, permanently bonding sculpture that was made in more than one piece and fixing broken sculpture: Broken sculpture that has clean edges that fit well together can be fixed by using 5 minute epoxy, that kind that comes in two tubes that you mix together.Then to cover the crack , and also to fix cracks in other sculpture, use DAP pre-mixed cement. It comes in a quart container and is grey in color. Use acrylic paints to color the cement to match the sculpture clay, or glaze. It can take a little practice. Work the cement into the crack and let sit 2-3 minutes, then sponge away so only the crack is filled. If it is a really wide crack, say 1/2 inch, the cement may shrink a bit. Let dry a couple of days then reapply. Attached separate pieces of sculpture together using the cement. Let dry about a week. The pieces will be very well bonded!
For repairing non-structural cracks: by Pete Pinnell: http://www.claytimes.com/articles/glazeadjusting.html
My general advice is to leave the cracks or breaks for post-firing repair. However, as long as the crack is not structural, I have had great success in healing them by packing them with bisqued clay dust and some sort of flux. *With every piece* I place a small amount of sieved powdered clay next to it in the kiln. After the bisque firing, the clay powder may be mixed with the glaze or vitreous slip and packed into the crack. After it has dried, wipe smooth and apply the normal surface treatment over the whole piece. I also fire the remaining bisqued powder with the piece through the second firing and use it again to mix with epoxy for post-firing repairs.
GLUES: For gluing joints together or strength bonds: Devcon 5- Minute Epoxie Gel. This is some of the toughest stuff . There are tons of other high strength epoxies out there, but use one that can easily find locally. Check to make sure it hasn’t been sitting on the shelf of the hardware store for more than a year. Most glues have a shelf life and should be purchased as needed. Stronger than your clay, little to no yellowing, and no dripping. Make sure you mix it to death! Use Popsicle sticks and squares of tinfoil for mixing.
To join large sections together, use the one hour slow setting epoxy mix on the inside edge of the seam, and then tack it in place with the five minute gel on the outside edge of the seam. The slow setting epoxy will have a bit more bonding strength since it penetrates the pores of the clay more thoroughly.
For filling seams or cracks: Apoxie Sculpt two part kneadable Epoxy. Purchase the white so that you are able to tint it yourself by kneading in mason stains and fired clay powder. This stuff is great for mimicking texture and color. Long working time- sets in 2-3 hours, with full strength in 12-24 hours. Order it from WASCO taxidermy supply at: www.taxidermy.com
Faster setting kneadable epoxies: East Valley kneadable Epoxy. Just like the material above, this is a two part epoxy mixed with clay, so that it is less likely to yellow or change color over time. It sets rock-hard in one hour and can be sanded, drilled, or painted. The company who sells this, also sells pigments you may mix with the epoxy to change the color to match your clay, glaze, or slip surface: http://www.eastvalleyepoxy.com/.
In an emergency,use the ACE Hardware Brand grey plumber’s kneadable epoxy. It sets in five minutes, which is great, but it barely leaves enough time to knead in the mason stains and mix thoroughly before applying it to the surface. Use this on the bottoms of pieces as ‘bumpers’ to level them off. Wax paper on the table helps to keep it from sticking.
Beth Cavener Stichter’s website has more information, http://www.followtheblackrabbit.com/material.htm. Glues are under “Other Materials”